1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery.
2. Background Art
The nonaqueous electrolyte secondary battery has been used in a power supply unit of an electronic apparatus, an electric power storage unit that absorbs a variation in electric power generation of a power generator, and the like. Particularly, a small-sized nonaqueous electrolyte secondary battery such as a coin-type (button-type) battery, has been widely employed in portable devices as a power supply for motor driving and the like, in addition to a backup power supply as a timepiece function, a backup power supply of a semiconductor memory, an auxiliary power supply of an electronic device such as a microcomputer and an IC memory, and a battery of a solar timepiece (for example, refer to JP-A-2000-243449). The coin-type nonaqueous electrolyte secondary battery employs, for example, a structure in which a positive electrode, a negative electrode, and an electrolyte are accommodated in an accommodation space surrounded by a bottomed cylindrical positive electrode casing and a negative electrode casing, and the positive electrode is electrically connected to the positive electrode casing, and the negative electrode is electrically connected to the negative electrode casing. In addition, a gasket is interposed between the positive electrode casing and the negative electrode casing, and the space between the positive electrode casing and the negative electrode casing are caulked to seal the accommodation space of the nonaqueous electrolyte secondary battery.
In addition, recently, application of the coin-type nonaqueous electrolyte secondary battery, for example, to a power supply of an electric vehicle, an auxiliary electric power storage unit of an energy converting and storage system, and the like has been examined. Particularly, in a case where a lithium manganese oxide is used as a positive electrode active material, and a silicon oxide (SiOX) is used as a negative electrode active material, it is possible to obtain a nonaqueous electrolyte secondary battery in which charging and discharging characteristics are excellent with a high energy density, and a cycle lifetime is long.
Here, in a case where a non-reflow type nonaqueous electrolyte secondary battery of the related art is used for backup of a memory of a portable phone or a digital camera, an operation guarantee temperature range is −20° C. to 60° C. On the other hand, recently, realization of a nonaqueous electrolyte secondary battery, which can be used for an electronic component of an in-vehicle component such as a drive recorder under a high-temperature environment of 80° C. or higher, has been expected. However, when the nonaqueous electrolyte secondary battery is used under the high-temperature environment, an electrolytic solution inside the battery volatilizes, and lithium deteriorates due to intrusion of moisture into the battery, and thus there is a problem in that capacity greatly deteriorates.
To suppress the volatilization of the electrolytic solution from the inside of the nonaqueous electrolyte secondary battery under the high-temperature environment or the intrusion of moisture into the inside of the battery as described above, there is suggested a technology of setting a region, in which a compression ratio of the gasket interposed between the positive electrode casing and the negative electrode casing is in a predetermined range, at two or more sites around the entire periphery of the gasket (for example, refer to JP-A-58-135569).
In addition, with regard to the nonaqueous electrolyte secondary battery, there is suggested a technology in which the compression ratio of the gasket interposed between the positive electrode casing and the negative electrode casing is set to a predetermined range at three-point positions between a tip end of the positive electrode casing and the negative electrode casing, between a tip end of the negative electrode casing and the positive electrode casing, and between a folded tip end of the negative electrode casing and the positive electrode casing, and the magnitudes of compression ratios at the respective three-point positions are set in this order (for example, refer to JP-A-9-283102).
JP-A-58-135569 and JP-A-9-283102 disclose that when the compression ratio of the gasket interposed between the positive electrode casing and the negative electrode casing is set to a predetermined range, the following effects can be expected. Specifically, sealing properties of the nonaqueous electrolyte secondary battery can be raised, leakage of an electrolytic solution can be suppressed, and intrusion of moisture can be suppressed.